1. Field of the Invention
The present invention relates to a music-signal compressing apparatus that records a music signal by controlling a compression method according to a part thereof, a music-signal decompressing apparatus that decompresses the signal, and a music-signal compressing/decompressing apparatus that records or reproduces the music signal by controlling compression and decompression methods.
2. Discussion of the Related Art
Generally, a music signal is composed of a plurality of parts representing, for example, melody sound and rhythm sound, or vocal sound and accompany sound, which are different in musical semantics. In listening to music, a human being is capable of separately recognize each of the plurality of parts through psychoacoustic processing. In addition, in most cases, human-being auditory senses for these individual parts are not uniform, and they are greatly different depending on musical importance. In more specific, it can be considered that, in many cases, an ordinary human listener enjoying music concentrates his/her senses on, for example, melody sound and vocal sound. This is equivalent to a case where an auditory masking phenomenon occurs between multiple audio sources.
In conventional compression methods, compression processing is performed using the same algorithm even when, for example, a music signal to be compressed is composed of a plurality of parts as those described above, and a music signal does not have, for example, musical semantics or a musical structure as in the case of a single audio source.
However, in the conventional compression methods as described above, the compression-encoding data rate is allocated without distinction either to a signal component of a part having high musical importance or to a signal component of a part not having high musical importance. As such, when the compression rate is increased, quality of reproduced audio is degraded at the same level both in the signal component having high musical importance and in the signal component not having high musical importance without distinction.
An object of the present invention is to realize a music-signal compressing apparatus, a music-signal decompressing apparatus, and a music-signal compressing/decompressing apparatus in which the data rate to be allocated to a signal component of a part having high musical importance in compressed data can be increased to be relatively high in comparison to the case of compressed data in conventional methods.
A music-signal compressing/decompressing apparatus of the present invention includes a music-signal input section, a preprocessing section, a data-compressing section, a data-storage section, and a music-signal output section. The music-signal input section inputs a music signal. The preprocessing section preprocesses an output signal of the music-signal input section at a stage preceding compression processing. The data-compressing section performs compression processing for an output signal of the preprocessing section. The data-storage section stores data compressed by the data-compressing section. The data-decompressing section performs decompression processing for compressed data read out of the data-storage section. The music-signal output section outputs an output data of the data-decompressing section as a music signal. The preprocessing section includes an audio-source separating section for performing separation processing to separate the output signal of the music-signal input section into signals in units of the type of audio source; a physical-property converting section for performing physical-property converting processing to change a physical property of each of the signals separated by the audio-source separating section; a signal-synthesizing section for synthesizing a plurality of signals that have been outputted from the physical-property converting section; a control-information input section for inputting control information regarding the contents of the audio-source separation processing performed by the audio-source separating section and the contents of the physical-property converting processing; and a preprocess control section for performing control of the audio-source separating section and the physical-property converting section according to control information that has been outputted from the control-information input section.
The music-signal compressing/decompressing apparatus may be configured in which the preprocessing section further comprises audio-source analyzing section which performs analysis of the physical property of at least one of the signals separated by the audio-source separating section; the physical-property converting section which inputs an output signal of the audio-source analyzing section, and performs the physical-property converting processing according to the output signal for changing the physical property of at least one of the signals separated by the audio-source separating section; and the preprocess control section which performs control of the audio-source separating section and the physical-property converting section according to analysis-result data that has been outputted from the audio-source analyzing section and the control information that has been outputted from the control-information input section.
In consideration regarding human psychoacoustic processing, signal processing is performed for a signal component that has low musical importance to reduce a part of an energy component thereof, and thereafter, compression processing is performed.